text: Surface tension is dependent on temperature. For that reason, when a value is given for the surface tension of an interface, temperature must be explicitly stated. The general trend is that surface tension decreases with the increase of temperature, reaching a value of 0 at the critical temperature. For further details see Eötvös rule. There are only empirical equations to relate surface tension and temperature:
  * Eötvös:  Here  is the molar volume of a substance,  is the critical temperature and  is a constant valid for almost all substances. A typical value is  = . For water one can further use  = 18 ml/mol and  = 647 K (374 °C). A variant on Eötvös is described by Ramay and Shields:  where the temperature offset of 6 K provides the formula with a better fit to reality at lower temperatures.
  * Guggenheim–Katayama:   is a constant for each liquid and  is an empirical factor, whose value is  for organic liquids. This equation was also proposed by van der Waals, who further proposed that  could be given by the expression  where  is a universal constant for all liquids, and  is the critical pressure of the liquid (although later experiments found  to vary to some degree from one liquid to another).
  Both Guggenheim–Katayama and Eötvös take into account the fact that surface tension reaches 0 at the critical temperature, whereas Ramay and Shields fails to match reality at this endpoint.